1. Field of the Invention
The present invention relates to a drive transmission system provided with a one-way clutch which rotates by being driven like a separation roller that moves the cut paper of a facsimile device for example, and idles when rotated in an advancement direction faster than the rotational velocity.
2. Description of the Related Art
For example, on a document supply system of a facsimile device, a document is set in the tray, sent in the direction of an image sensor and scanning is carried out. Accordingly, the following occurs in sequential order. As shown in FIG. 11, the separation roller 71 is driven and a bottom-most document G is sent downstream. When the document G is initially transported along the movement pathway, a passage sensor 72 detects the leading edge of the paper. The document G being moved along the movement pathway then arrives at the conveyance roller 74. The rotational velocity of the conveyance roller 74 is set slightly faster than that of the separation roller 71 and as a result of difference in velocity, the document G is pulled downstream by the conveyance roller 74. As a result, a difference in the conveyance speed between the first document and the next document delivered by the separation roller 71 is generated, thus forming a gap between the documents G. As a result of this, the passage sensor 72 is able to detect the trailing edge of the document G currently being transported and accordingly, the size and number of pages of the scanned document may be detected. Thus, in order to allow the pulling of the document G when pulled by the conveyance roller 74, a one-way clutch system is provided wherein the separation roller 71 idles with respect to the rotation in the advancement direction.
On conventional systems as shown in FIGS. 12A and 12B, a clutch spring 77 is attached to a metal shaft 75 attached to the separation roller 71. This clutch spring 77 is fitted into the drive gear 78 so that it moves freely. When the drive force of the gear 78 is transmitted to the shaft 75, the clutch spring 77 is reduced in diameter and contacts the outer periphery 78a of the cylindrical base of the gear 78. Thus, driving is transmitted to the shaft 75 via the clutch spring 77. Conversely, if the separation roller 71 is allowed to rotate freely in an advancement direction, the clutch spring 77 expands and does not come into contact with the outer periphery 78a of the cylindrical base of the gear 78. In short, when the separation roller 71 is rotated in the advancement direction, the shaft 75 freely rotates without driving being transmitted to the shaft 75.
Furthermore, there are also conventional driving systems not having one-way clutch systems as shown in FIGS. 13A and 13B. This involves the arrangement of a first engagement peg 80 on one part of the outer periphery of a resinous shaft 79 attached to the separation roller 71 and the arrangement of a second engagement peg 82 on one part of the outer periphery of the drive side gear shaft 81. When the driving is transmitted from the gear shaft 81 to the shaft 79, the second engagement peg 82 contacts the first engagement peg 80 from behind and both pegs engage together. Then driving is transmitted by the second engagement peg 82 pushing the first engagement peg 80 when the gear shaft 81 rotates. Conversely, when the rotation of the shaft 79 is faster than the rotation of the gear shaft 81 due to the document G being pulled by the conveyance roller 74, as the separation roller 71 starts freely rotating in the advancement direction, the first engagement peg 80 separates from the second engagement peg 82. Then, if the separation roller 71 (shaft 79) makes approximately one revolution ahead of the gear shaft 81, the first engagement peg 80 engages with the second engagement peg 82. When the document G is ejected from the conveyance roller 74, the separation roller 71 stops. At that time, even if the gear shaft 81 rotates, the separation roller 71 stays in a stopped state until the second engagement peg 82 has once again engaged with the first engagement peg 80 by rotating 360 degrees. Then the document G delivery operation is repeated with the second engagement peg 82 once again in contact with the first engagement peg 80 from behind.
However, the following problems exist with the drive transmission systems as described above.
(1) On the system shown in FIGS. 12A and 12B: PA1 (2) On the system shown in FIGS. 13A and 13B;
a. Clutch spring 77 is used as the necessary part of the one-way clutch system but this part has comparatively high costs, PA2 b. As contact is made with the outer periphery 78a of the cylindrical base of the gear 78 due to slight changes in diameter, a high degree of precision is required for the dimensions of the part, PA2 c. Time is required for the contact operation of the clutch spring 77, PA2 d. Abrasion of the outer periphery 78a of the gear 78 occurs over the passage of time as the clutch spring 77 transmits the driving by friction, PA2 e. As the drive transmission is carried out by friction, leakage of machine oil would cause free rotation resulting in unreliable transmission leading to instability in the operations, and PA2 f. Permeation of water causes rusting, etc.
When the rotation of the shaft 79 is faster than the rotation of the gear shaft 81, if the separation roller 71 (shaft 79) makes one rotation ahead of the gear shaft 81, the first engagement peg 80 of the shaft 79 engages with the second engagement peg 82 of the gear shaft 81. In short, because this is not a one-way clutch system, a load from the gear shaft 81 (being a braking action) is normally exerted on the separation roller 71 (shaft 79) when driving in the advancement direction is applied from the conveyance roller 74. Accordingly, the drive transmission force is wastefully expended and heating due to overload may also arise.